Single-Crystal X-Ray Diffraction of Minerals to Mbar Pressures

晶体结构是矿物最基本的特性。结构和成分决定了矿物。S的物理和化学行为。在地球的高压条件下？在深部内部，矿物经常经历相变，形成新的、更致密的晶体结构。这个项目的目的是利用先进的实验技术来研究地球上一些最丰富的矿物在高压下晶体结构的演变。S上地幔。压力将使用金刚石砧细胞产生，这是一种装置，其中样品被挤压在小钻石的尖端之间。晶体结构由同步辐射设备发射的强大x射线束探测。要研究的矿物包括地球上的主要矿物？S上地幔：橄榄石、辉石和石榴石。这项工作将导致新的晶体结构的发现，这与理解这些重要的地球材料的高压行为有关。我们将使用基于同步加速器的单晶x射线衍射技术来研究地幔矿物在高达1毫巴（100 GPa）压力下的晶体结构和状态方程。与更标准的粉末x射线衍射技术相比，单晶方法具有许多优点。首先，我们收集了基于同步加速器的合成橄榄石Mg2SiO4的单晶x射线衍射，并在50 GPa下观察到以前未知的相变。通过在几乎各向同性的氦传压介质中使用小晶体，可以在相变中保留单晶。这为获得高压相的晶格参数、状态方程和晶体结构的精确约束提供了机会。我们还将致力于利用外部和激光加热技术将能力扩展到同时高P-T条件。新的单晶x射线技术的应用有可能成为高压研究的重大进展。

The crystal structure is the most fundamental property of a mineral. The structure along with composition determines the mineral?s physical and chemical behavior. Under high-pressure conditions of Earth?s deep interior, minerals often undergo phase transformations to new, denser crystal structures. The purpose of this project is to use advanced experimental techniques to study the evolution of crystal structures under high pressures for some of the most abundant minerals of the Earth?s upper mantle. Pressure will be generated using a diamond anvil cell which is a device in which the sample is squeezed between the tips of small diamonds. The crystal structure is probed with a powerful X-ray beam from a synchrotron radiation facility. Minerals to be studied include the major minerals of Earth?s upper mantle: olivine, pyroxene, and garnet. The work will lead to the discovery of new crystal structures which are relevant for understanding the high-pressure behavior of these important Earth materials. We will use synchrotron-based single-crystal X-ray diffraction techniques to examine the crystal structure and equation of state of mantle minerals to pressures up to 1 Mbar (100 GPa). Compared to more standard powder X-ray diffraction techniques, single-crystal methods have many advantages. Initially, we have collected synchrotron-based single-crystal X-ray diffraction on synthetic olivine, Mg2SiO4, and observed a previously unknown phase transition at 50 GPa. By using small crystals in a nearly isotropic helium pressure-transmitting medium, it is possible to retain single crystals across phase transitions. This opens the opportunity to obtain precise constraints on the lattice parameters, equation of state, and crystal structure of high-pressure phases. We will also work on extending capabilities to simultaneous high P-T conditions using external and laser heating techniques. The application of new single-crystal X-ray techniques has the potential to be a major advance in high-pressure research.